The traditional single coil magnetic pickup for stringed musical instruments as originally designed and offered by Fender Musical Instruments Corp. consists of a coil form with alnico magnets as its core that is wound with numerous turns of copper wire. This design set the standard for reproducing what is commonly known and recognized today as the Fender sound. Inherent to this original work are certain design choices that have been well documented and in some cases addressed to various degrees by other pickup designs. To some degree, many early pickup designs have been susceptibility to external electromagnetic radiation and the magnetic interference with the natural vibrations of the strings.
To address the electromagnetic interference, hum canceling coils, also known as humbucking coils, have been used in pickup designs. Hum canceling coils have been known since 1825 when Leopoldo Nobili invented the astatic galvanometer; where it is stated: “Two identical coils of N turns are connected in series, in such a way, that the current passes through them in opposite senses to neutralize external magnetic fields”. Collinear coil assemblies for electrical musical instruments have been known since the mid 1930s, with U.S. Pat. No. 2,119,584 most likely representing the first such patent. Many early pickup designs, due to the extremely small market demand at the time, were never patented.
Magnetic pickups of various designs have been used in the sound reproduction of stringed musical instruments since 1930. They are generally placed directly under the strings between the bridge and the end of the fingerboard of the instrument. In simplest terms, the electromagnetic pickup in combination with the vibrating string represents a multi-frequency voltage generator. Magnetic pickups are an important component in what makes up the sound characteristics of a given amplified electric stringed musical instrument. Certain companies that manufacture these instruments have developed magnetic pickups that have contributed to what has become known over time as their signature sound. The acknowledgement of this sound signature has to be considered in the design of any new instrument and its component parts including the design of the pickup.
Based on changes that had taken place in musical instrument amplification (for example, digital sound recording equipment; computer interface for stringed musical instruments; changes in playing techniques and styles of music), Fender requested, in 1996, the development of a high performance electromagnetic pickup.
The pickup had to meet the following demands: (1) to not exceed the dimensions of Fender's traditional single coil pickups; (2) to generate a higher output voltage than their traditional single coil pickups; (3) to reproduce the legendary signature sound of their traditional single coil pickups; (4) to increase sensitivity to minute amplification adjustments allowing the player to select from a wider tonal variety; (5) to reduce the magnetic force directed towards the strings so as to minimize magnetic interference with the vibrating strings; (6) to neutralize the interference of external electromagnetic radiation; and (7) to be manufactured cost effectively.
These demands presented several major problems. To increase the output requires either stronger permanent magnets or more turns of wire. Stronger permanent magnets, due to their high coercive force, have negative solenoidal qualities. When placed close to the core of a solenoid they will cause magnetic saturation of the core resulting in a dramatic loss of their relative permeability and in addition will cause a strong magnetic interference with the vibrating string. More turns of wire would not only increase the impedance, resulting in a shift to undesired frequencies, but would also require a larger coil dimension. It was also important to consider that a vibrating string does not produce a pure tone that can be explained with the single curve of a sine wave. The tone of a vibrating string consists of several different sine waves, resulting in a complex waveform that can be found by adding the ordinates of all its component sine waves. This complex waveform represents the Fourier spectrum of a tone, which musicians simply call the “signature sound”. The Fourier spectrum depends partially on the position of a pickup in relation to the bridge of the instrument and the position, angle, and force of the attack. However, the most important factor is that the signal generated above the coil is in-phase with the signal generated at the sides of the coil.
A need exists to eliminate the negative functions of magnetic structures used in collinear coil assemblies.